Chopped, glass fiber strands are typically manufactured by either direct or indirect processing operations. Direct processing operations (or "direct-chop" operations) involve feeding a generally continuous, glass fiber strand directly from a fiber forming assembly into a chopping assembly where the strand is chopped. Indirect processing operations involve winding a generally continuous fiber strand onto a tube to form a package and subsequently feeding the generally continuous strand from the package into a chopping assembly. Packages of generally continuous fiber strand can also undergo additional processing steps, such as roving wherein multiple packages are combined into one package, prior to being chopped. Since direct processing of generally continuous fiber strands into chopped fiber strands reduces manufacturing costs by eliminating unnecessary processing and handling steps, it is often the preferred manufacturing route.
In direct-chop operations, a plurality of generally continuous, individual glass filaments are drawn from a fiber forming apparatus, such as a heated metal bushing or spinneret, and bundled together by a gathering device to form a generally continuous fiber strand. Before bundling the filaments together, a coating composition or sizing is applied to at least a portion of the surface of the individual filaments to protect them from abrasion. As used herein, "sizing" or "size" refers to a coating composition applied to the filaments immediately after forming. Such compositions are well known to those skilled in the art and are disclosed in K. Loewenstein, The Manufacturing Technology of Glass Fibers, (3rd. Ed. 1993) at pages 237-289, which are hereby incorporated by reference. After bundling, the generally continuous fiber strand is chopped to form a plurality of discrete, chopped strands. These wet chopped strands are then processed through a dying oven to at least partially dry the size on the surfaces thereof.
Transferring the wet, chopped strands to a drying oven can be done by collecting the chopped strands in a container or tote immediately after chopping and transporting the totes to a drying oven. This process is undesirable, however, due to the labor and handling associated with moving the totes. Furthermore, agglomeration or sticking of the wet, chopped strands can occur due to contact between strands having undried size on at least a portion of their surfaces.
An alternative method of transporting wet, chopped strands to a drying oven involves the use of a conveyance system, such as a conveyor belt. In this method, immediately after chopping, the wet strands are deposited directly onto a conveyor belt which transports them to a drying oven. While this method reduces the labor and handling associated with the use of totes, it does not eliminate the agglomeration concerns. Additionally, adherence of the wet, chopped strands to components of the conveyance system, such as the conveyor belt, can occur.
Agglomeration or sticking of the wet, chopped strands to each other and/or the equipment is undesirable because the strand bundles tend to break apart or filamentize when the strands are finally separated. Filamentization or breakage of the strand bundles is detrimental to the processing and handling characteristics of the strands in subsequent processing operations, such as but not limited to compounding and molding. Additionally, the properties of final products, such as reinforced plastic articles made using the strands, can be adversely affected.
As discussed below, several patents have been directed toward improving chopped strand manufacture operations and the quality of the product produced therefrom.
U.S. Pat. No. 3,996,032 discloses the use of a series of vibrating conveyor belts in the manufacture of chopped strands. After being chopped, strands fall onto a first vibrating conveyor which agitates the chopped strands (col. 2, lines 52-56). Subsequently, the strands are passed to a second vibrating conveyor having an amplitude of vibration less then that of the first conveyor (col. 2, lines 59-62). The second conveyor has a heating zone associated therewith to reduce the moisture content of the chopped strands (col. 2, 62-67).
U.S. Pat. No. 4,840,755 discloses the use of a spheroidizing or rolling apparatus to form chopped strands having a rod-like shape. Chopped strands formed by a cutting device are dropped onto a spheroidizing plate and subjected to a rolling action by a vibrating plate (col. 5, lines 42-45). The rolling action causes rounding and compacting of the strands into a rod-like shapes (col. 6, lines 26-31). After rolling, the strands are transferred to a drying station, either directly through an opening in the rolling apparatus or indirectly by means of a transfer device (col. 5, lines 27-30).
Japanese Kokai Application No. H4-164838 discloses the use of a vibrating conveyance device to transport wet, chopped strands from a cutter to a dryer. After being cut, the wet, chopped strands fall onto a vibrating conveyor attached at an angle to the intake mouth of a dryer and are fed to the dryer without accumulation or adherence of the strands to the conveyor. (page 4, paragraphs 3-4).
The foregoing references, however, do not provide a means for manufacturing dried, chopped strands that eliminates the need for external conveyance systems while improving product quality and reducing labor and equipment costs.